This invention relates generally to gas turbine engines, and more particularly to methods and apparatus for fabricating a coating for gas turbine engine blades.
At least some known gas turbine engines include one or more turbine rotors, which include a rotor disk and a plurality of circumferentially-spaced rotor blades, sometimes referred to as blades. Known blades typically include an airfoil, a platform, a shank, and a dovetail. Each dovetail is received within a slot or opening defined in the rotor disk to secure the blades to the rotor disk. The airfoils extend from the disk into the flow of combustion gases within the engine and convert kinetic energy of the gas flow into rotational mechanical energy.
Fouling and surface degradation generally occur when as the result of burning fuels containing alkali metals that combine with sulfur during the combustion process and deposit low melting salts on the surface of the parts. Additional contaminants may come from air ingested and/or water injected for NOx control or power augmentation.
To facilitate protecting the blades during engine operation, at least some known turbine engine blades include a thermal barrier coating (TBC). However, known thermal barrier coatings sometimes have a relatively rough outer surface, and as such, some thermal barrier coatings may be prone to erosion caused by, for example, the adherence of contaminants, such as low melting salts or other contaminants that may be generated during combustion. Erosion of the thermal barrier coating may reduce effectiveness of the thermal barrier coating and/or may exacerbate further erosion, which may lead to even further performance degradation.
To facilitate reducing the effects of the rough outer surface of the TBC, at least some thermal barrier coatings are hand-polished to reduce the surface roughness and increase the erosion resistance of the thermal barrier coating. Hand polishing may increase the time, and/or effort, involved in fabricating turbine blades, and/or may increase the likelihood of human error during fabrication of the turbine blades. As a result, an overall cost of fabricating gas turbine engines including hand-polished blades may be higher than costs associated with fabricating other blades that are not hand-polished.